The next step of preparation is to sanitize and chill the bottles to the same temperature as the beer. I used a little foil on top to keep any funk out. I chilled the bottles about 2 hours before hand, just to make sure they were good and cold. Having the bottles a little wet inside is a good thing, as it will prevent excessive foaming during the fill.
This is the disassembled Beergun in Starsan. I needed the instructions to set it up the first few times, as it just looks like a mess of bolts and rods when taken apart. One thing to note is that I used Saniclean one time to sanitize, and it left some funky looking black stains on certain parts of the Beergun that I'm sure were not harmful, but they were ugly.
I use a mason jar filled with Starsan to hold the Beergun while I am capping. Here it is with the CO2 purge-line and liquid line attached. You want to keep as much of the liquid line cold as possible, so make sure to put any excess tubing inside the kegerator.
I've got my little work-station set up here with bottle caps, a spill tray, and a cat litter box to sit on. Take note: I am a lefty, so if you are a righty, you'll want all that stuff on your right side.
I take the bottles out a few at a time, purge them for a few seconds with gas, and fill away. I have the CO2 regulator set at 4 PSI, which seems to give a decent rate of flow without too much foam-up.
Here you can see there is some minimal foam, but actual beer loss is very low. As the bottle fills, I lift the Beergun up towards the neck. When it is full, I do not purge the neck with C02 as the instructions say. Instead, I just make sure to cap on foam. It's all CO2 anyway.
You can get a pretty consistent fill level, and you should cap the bottles one at a time. Get a helper if you want to go really fast.
Here is the case of bottles I filled, plus a 1 liter bottle, and the waste comes out to about 2-3 ounces (that is an 8 ounce cup at most). The actual filling took about 12 minutes. Prep and cleanup is very quick, as long as your bottles are clean already.